Traditionally, plastic eyeglass lenses as well as plastic lenses designed for other applications have been fabricated by one of two ways: 1) casting the whole lens between two molds as a finished monolithic optic; and 2) casting a semi finished blank, then grinding it to the desired prescription. Both thermoplastics and thermosets may be used as optical materials. Thermoplastics are generally formed by injection molding, although compression and transfer molding techniques have also been used. Thermosets, such as resin formulations based on diethylene glycol bis allyl carbonate (DEG BAC) are formed by cast molding techniques. In all cases, what is obtained is a finished optic made of a single material. This optic may subsequently be coated to develop desired surface properties, such as enhanced scratch resistance, reduced optical reflectance, or enhanced impact resistance, mostly using conventional coating processes, such as dip coating, spin coating, or vacuum deposition. These coatings rarely exceed 25 microns in thickness.
Recently, methods of casting optical layers of a wide range of thicknesses on lenses have been disclosed, e.g., by Blum (U.S. Pat. No. 5,219,497). These methods utilize a substrate lens blank and a mold of specified curvature to polymerize a liquid resin on the surface of the lens substrate. The layer may be uniform in thickness, or may alter the surface geometry of the substrate in some specified and controlled manner. Layers of 1,000 microns or more at the upper end, and down to 25 microns in thickness may be deposited by this method. This method is applicable to both thermoplastic and thermoset lens substrates, and both thermoplastic and thermoset layers may be deposited through the use of a mold. A layered composite optic may be formed by this method.
The cast optical layers in thickness between 25 and 1000 microns or more may perform many optical functions. They may be added to minimize optical aberrations in the substrate lens blank, develop an achromatic optic or provide bifocal or multifocal optics through the development of refractive index gradients. The superstrate layers may also be provided to add a photochromic layer to the substrate lens blank. Indeed, the quality and range of applicability of plastic lenses is significantly enhanced by the development of composite optics, formed by adding one or more layers on a lens substrate.
Although the fabrication of composite lenses using a mold and a lens blank as described above is well established, the fabrication method requires a large inventory of molds and a separate fabrication facility in addition to the one used to cast the substrate blanks. It is therefore desirable to develop a fabrication process in which the development of the superstrate layers is integrated to the manufacture of the lens blanks themselves, and does not require additional handling of the blanks after they are formed. Previously disclosed methods of formation of photochromic lenses (U.S. Pat. No. 4,968,454 by Crano et al., U.S. Pat. No. 4,286,957 by Le Naour-Sene, U.S. Pat. No. 4,936,995 by Kwiatkowski, and U.S. Pat. No. 4,637,698 by Kwak, et al.) have included application of photochromic layers on lenses or lens blanks, but have not addressed the integration of the photochromic layer to the substrate, in order to arrive at a streamlined manufacturing process at a lower cost, or to achieve a superior optical quality as well as mechanical and thermal properties by developing an interphase between the lens substrate and the superstrate layer.